(CNN) - Secretary of State Mike Pompeo said Friday that the US is looking into reports that North Korea executed a top official after President Donald Trump and Kim Jong Un's summit in Hanoi, Vietnam, earlier this year.
South Korean newspaper Chosun Ilbo reported that Kim Hyok Chol, North Korea's special envoy to the US, was executed after Kim Jong Un and Trump were unable to reach an agreement at their second summit in February.
"We've seen the reporting ... we're doing our best to check it out," Pompeo said during a joint press conference with the German Foreign Minister Heiko Maas in Berlin.
CNN has not been able to independently verify the reporting in Chosun Ilbo -- South Korea's most-circulated daily newspaper -- and South Korean reports of North Korean executions have at times been inaccurate.
The paper -- quoting unnamed North Korean sources -- said Kim Hyok Chol was executed in March at the Mirim airport in Pyongyang on charges of "being recruited by US imperialists and betraying the supreme leader."
Kim Hyok Chol, North Korea's State Affairs Commission special representative, led negotiations with the US special representative to North Korea, Stephen Biegun, at the Hanoi summit and was in charge of the working-level talks with American counterparts.
White House press secretary Sarah Sanders would not comment on the Chosun report Friday but did say the US is "monitoring the situation."
"I'm not going to comment on intelligence one way or another. I can tell you that we're monitoring the situation and continuing to stay focused on our ultimate goal, which is denuclearization," she told reporters.
South Korea's Presidential Blue House echoed that message, saying: "We do examine all relevant information, but we think that it is important to grasp how much of confirmed information the article contains. I do not think it is appropriate to make any hasty judgment or comment about that part."
A senior diplomatic source with knowledge of the situation told CNN that Kim Hyok Chol and Kim Yong Chol "have certainly disappeared," but there is "no independent information or intelligence at this point on what's happened."
In the past, North Korean officials have disappeared, only to resurface after a period of "re-education," the source noted.
Kim purging top officials?
In addition to reportedly executing Kim Hyok Chol, North Korea's leader is believed to be carrying out a purge of top officials following the failure of the negotiations with the Trump administration, the paper said.
Kim Yong Chol, one of North Korea's top negotiators who accompanied Kim to both summits with the US President, was reportedly "dismissed" and "is doing forced labor in Chagang-do province", according to Chosun.
Kim Yong Chol was the vice chairman of the Party Central Committee, and represented Kim Jong Un at key events as the young leader's top official in charge of relations between North and South Korea.
He also hand-delivered a letter from Kim Jong Un to Trump during a visit to Washington, DC, in January this year, and also served as Pompeo's counterpart in the negotiations.
His May 2018 trip to the US made him the most senior North Korean official to visit the country since 2000, when Vice Marshal Jo Myong Rok traveled to Washington to meet with then-President Bill Clinton in the Oval Office.
Shin Hye Yong, the interpreter for Kim Jong Un in Hanoi, was also reportedly imprisoned in a political camp for what Chosun described as an interpretation error at the summit. Her mistake "damaged the authority" of the leader, according to the paper.
And Kim Song Hye, who was in charge of the working-level discussion with Kim Hyok Chol, was sent to a political prisoner camp.
Kim Jong Un's sister Kim Yo Jong, who was by his side in Hanoi, was removed from official activity, Chosun reported.
Kim Yo Jong's profile has been steadily rising since 2014, when she given the key regime role of deputy director of the Propaganda and Agitation Department of the Workers' Party.
She was the face of the North Korean delegation at the Winter Olympics in South Korea last year, and had a seat at the table for the most significant peace talks between the two nations in decades.
In April, she was the only woman among six delegates at the historic talks between North and South Korea at the demilitarized zone (DMZ) that separates the two countries and is widely seen as instrumental in making the summit happen.
History of violence
While the details reported by Chosun remain unconfirmed, experts acknowledge that it is certainly plausible to think Kim Jong Un could have carried out a possible purge of this nature.
"There's certainly plenty of evidence -- both in Kim's recent past, and North Korean history -- of purging officials when things don't work out the way that the leader needs, or when there are potentially concerns about different factions within the government and the elite," according to Lindsey Ford of the Asia Society Policy Institute, who is also a former Pentagon adviser for Asian and Pacific Security.
"Trump can talk about how he and Kim are on the same page ... because they are buds, but (Kim) is a dictator who, in the past, has executed people close to him: his brother, his uncle -- and he's not afraid to do it again," Ford added.
Kim Jong Un is believed to have carried out hundreds of brutal executions since coming to power in December 2011.
North Korea's top education official Kim Yong Jin was executed by firing squad in 2016 after he exercised a "bad attitude" at the country's Supreme People's Assembly, according to a South Korean government official at the time.
In May 2015, Kim reportedly had his Defense Minister Hyon Yong Chol killed with an anti-aircraft gun at a military school in Pyongyang, in front of an audience.
Two years earlier, in 2013, Kim Jong Un's uncle was executed for trying to overthrow the government, according to state media, which described him as a "traitor for all ages."
Kim Jong Un has also been accused of ordering the assassination of his own half-brother, Kim Jong Nam, who had been living in exile from his homeland in the Chinese controlled territory of Macau and had occasionally criticized its regime.
North Korea has consistently denied involvement in the killing, though United States, South Korean and Malaysian authorities have said Pyongyang was responsible.
CNN's Sophie Jeong, Jake Kwon, Jennifer Hansler, Brian Todd and Dugald McConnell contributed reporting
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